1. Field of the Invention
The present invention relates generally to a printing press which performs printing by supplying an ink having a relatively high viscosity to a surface of a plate on a plate cylinder. More specifically, the invention relates to an ink supply unit in a keyless printing press constantly supplying an ink in a uniform thickness over an entire surface of a plate, which ink supply unit may prevent the ink accumulated therein while printing is interrupted, from leaking between a tip end of a blade and a fountain roller.
2. Description of the Related Art
An ink supply unit of a keyless printing press adapted for an ink having a relatively high viscosity has been disclosed in Japanese Unexamined Patent Publication No. Heisei 9-1780, entitled "Ink supply unit". In the above-identified publication, two ink supply units are disclosed. One ink supply unit is an ink supply unit dedicated to keyless printing. As shown in FIG. 8, the ink supply unit is constructed with an inking roller contacting with a peripheral surface of a plate surface on a plate cylinder P a metering roller K contacting with a peripheral surface of the inking roller and having a plurality of fine depressions uniformly distributed on a peripheral surface thereof, a doctor means D scraping off an excessive ink from a peripheral surface of the metering roller K, an ink supply unit 1' opened at an upper portion and a front portion and formed with both side plates and a tilted base, a fountain roller 2 located at a position closing the front side of the ink supply unit 1' and having a peripheral surface located in the vicinity of a front end edge of the base across a first gap 11, even number of ink rollers disposed between the fountain roller 2 and the metering roller K, opposing with a peripheral surface of the fountain roller 2 across a second gap 13, mutually contacting peripheral surfaces, and contacting with the metering roller K, and a separated water receptacle 40 provided below the ink supply unit 1' and the fountain roller 2.
As disclosed in prior art, the ink is removed from the ink supply unit 1' by means of the fountain roller 2. The excessive ink is scraped off from the peripheral surface of the metering roller K for supplying the ink on the surface of the plate in a substantially uniform amount over the entire width thereof.
On the other hand, when the excessive ink is scraped off, an excessive dampening water supplied to the surface of the plate by a dampening unit S, is admixed. The excessive dampening water admixed to the ink is separated from the ink by a shearing force exerted on the ink while the ink is led out through the first and second gaps 11 and 13 and drops into the separated water receptacle 40.
Another ink supply unit disclosed in the above-identified publication is an ink supply unit adapted for both keyless printing and non-keyless printing. In addition to the similar construction to the ink supply unit illustrated in FIG. 8, as set forth above, switching means capable of switching the doctor means D between a state in which the ink can be scraped off and a state in which the ink cannot be scraped off, and adjusting means capable of adjusting size of the first gap independently for respective zones arbitrarily divided along the axial direction of the fountain roller 2, are provided so as to make it possible to perform both keyless printing and non-keyless printing.
When keyless printing is to be performed by the ink supply unit constructed as set forth above, the doctor means D is placed in the state contacting with the peripheral surface of the metering roller K by the switching means, and, in conjunction therewith, the size of the first gap 11 is set to be maximum by the adjusting means, for enabling the keyless printing. Namely, similar to the foregoing, the ink is led out by the fountain roller 2 from the ink supply unit 1', the excessive ink is scraped off from the peripheral surface of the metering ink by the doctor means D to supply the ink on the surface of the plate on the plate cylinder P in a substantially uniform amount over the entire width. On the other hand, when non-keyless printing is to be performed, the doctor means is placed in the state located away from the peripheral surface of the metering roller K by the switching means, and in conjunction therewith, the first gap is adjusted to be fully opened position per each separated zone for adjusting the amount of the ink to be removed. Then, the ink is led out from the ink supply unit 1' by the fountain roller 2 and supplied to the surface of the plate on the plate cylinder P for respectively adjusting the amount per respective zones with increasing fluidability of the ink by passing respective rollers located in opposition for cooperation.
In the case of the ink supply unit dedicated for keyless printing, the first gap 11 between the front edge of the ink supply unit 1' and the fountain roller 2 is invariable and is constantly opened. Therefore, while printing is interrupted, the stored ink leaks downwardly to frequently stain the peripheral components. Cleaning of such stain requires not an insignificant amount of work. Also, leakage inherently wastes the ink.
On the other hand, in the case of the ink supply unit for both keyless printing and non-keyless printing, the first gap 11 between the fountain roller 2 and the front edge of the base of the ink supply unit 1' is divided per divided zones along the axial direction of the fountain roller 2, and the adjusting means is provided for enabling independent adjustment of respective divided zones of the first gap.
When keyless printing is performed by the ink supply unit for both keyless printing and non-keyless printing, since the ink supply unit is used in the condition where the first gap 11 between the front edge of the base of the ink supply unit 1' and the peripheral surface of the fountain roller 2 are held open, the stored ink leaks downwardly to frequently stain the peripheral components, while printing is interrupted. In order to avoid leakage of the stored ink, it is possible to open and close the first gap 11 between the fountain roller 2 and the front edge of the base by the adjusting means per dividing zones to be used upon non-keyless printing.
However, the adjustment means for each divided zone inherently has a small and complicated operation mechanism. Furthermore, since the operation mechanism has to be provided for each divided zone, the adjustment means inherently becomes complicated and makes the production cost high. In addition, due to complicity of the mechanism and complicity of the means, frequency of occurrence of failure becomes high to make maintenance troublesome.